If the words that should be displayed in japanese are from a custom development, than transalation is not yet done. Don't think this is the problem, unless somebody created these objects who doesn't know any japanese.
If however, the text is from standard SAP, then probably not all texts have been translated yet. In this case you should contact SAP. In texts are not found in the login language, than normally the next available (logical) language will be used (normally this is english).
